COMPARATIVE‐ANATOMICAL STUDIES ON THE AMYGDALOID COMPLEX IN MAMMALS, ESPECIALLY IN UNGVLATA

The amygdaloid complex of Ungulata is not so well developed in comparison with that of Carnivora, but a more or less high degree of differentiation than in Rodents, especially in the nucleus T, which likely comes out from the cortical element during the early embryonal period. Cells of this nucleus have a tendency in the adult to get segregated in small glomerulus‐like groups, especially prominent in the cow. Another nuclei T' and M of amygdala proper are also well developed. But the central and medial nuclei E and D appear rather underdeveloped in comparison with those of Rodents. Although the small‐celled nucleus K is generally well developed and separated in numerous groups, the correspondent to the nucleus intercalatus of Rodents can not be detected in Ungulata. The degree of differentiation of periamygdaloid cortex is rather advanced as it is divisible here into 3 parts, PA1, PAi and Pam, very likely corresponding to Pam1, Pam2 and Pam3 of Rose respectively. The nucleus B is here completely separated from the cortex Pam PAi of the horse is complicated in its cellular architecture as it is divisible into two subdivisions. In the cow the whole extept of periamygdaloid cortex is complicated as in the nucleus T, both showing glomerulus‐like cell‐islets. If these complicated features speak for the advanced degree of differentiation of this region with its functional significance parallel going, then the cow or bull might be most developed among the animals concerned, then follow the goat, horse and pig in developmental order downwards. In accordance with the classification in taxology in Ruminantia (cow and goat) and Non‐Ruminantia (pig) of Archiodactyla and in Perissodactyla (horse), the cytoarchitectural patterns are each characteristic in these three groups. As to the fiber connection of the amygdaloid complex, the author has treated several fiber bundles of relatively well recognizable make‐up. Their exact origin and termination have however to be determined by experimental investigation later on. In fact there must be numerous and complicated fibers hitherto untouched by the authors. Indication lies here in this study of Ungulata as it introduced several fiber bundles hitherto unkndwn, seemingly favored by larger form of brains studied. Concerning the islet‐like groups of cells in the cow and goat, the author could not detect any specific fibrous characters even through application of certain axon‐staining method, except that of compactly arranged capsule‐like fibers. The assumption that the amygdala stands so intimately in relation with the cerebral cortex as the thalamus, or that it represents a vegetative centre or that it belongs to the extrapyramidal system, seems to be far from being entirely groundless as far as it concerns with the above mentioned anatomical investigation, but the lack of verification in experimental way leaves things to be entrusted to future researches.